Achromobacter denitrificans SP1 efficiently utilizes 16 phthalate diesters and their downstream products through protocatechuate 3,4-cleavage pathway.

This study provides physical and analytical evidences for the efficient utilization of most of the commercially available phthalate diesters by Achromobacter denitrificans SP1, coupled with the demonstration of a plausible degradation pathway. We tested 17 phthalate diesters [viz., ditridecyl phthalate, diisodecyl phthalate (DIDP), di(2-ethylhexyl)phthalate (DEHP), di-n-octyl phthalate (DOP), bis(2-ethylhexyl)isophthalate (BEIP), dihexyl phthalate (DHP), dibutyl phthalate (DBP), dicyclohexyl phthalate (DCHP), diphenyl phthalate (DPP), benzyl butyl phthalate (BBP), diamyl phthalate (DAmP), diisobutyl phthalate, dipropyl phthalate, dially phthalate (DAlP), diethyl phthalate, diethyl terephthalate and dimethyl phthalate (DMP)], and their major degradation products for the degradation efficiency of A. denitrificans SP1 in Wx medium. It efficiently utilized 16 phthalate diesters (except DAlP), and showed general preference toward phthalate diesters with longer side chains (utilized ~10mM in 48h) than those with shorter side chains and with cyclic structures (utilized ~5mM in 48h) accompanied by a sharp decline of pH to ~5 from initial 7. In a detailed study, about 37mM (~15g/L) DEHP was utilized in 48h. Moreover, A. denitrificans SP1 produced reddish-pink pigment when DIDP, DEHP, DOP, DHP, DBP, DIBP, BBP, DAmP, DCHP, DPP or DMP was supplied in the medium. From the available evidences, it seems that its putative phthalate diester degradation pathway contains the following check points: phthalate diesters, phthalate monoesters, phthalate (4,5-dioxygenase), protocatechuate (3,4-dioxygenase), and TCA cycle. Nonspecificity toward utilization of phthalate diesters, especially with greater specificity to phthalate diesters having longer side chain, and the characteristic sticky reddish-pink (or colorless) cell clump formation in the presence of phthalate diesters makes A. denitrificans SP1 a very attractive candidate to be employed as an efficient biofactory in waste water treatment processes.